The invention relates to a device and a method for guiding surgical tools by ultrasonic imaging. The device and method of the invention are particularly applicable to ultrasonically guided minimally invasive surgery and are especially aimed at avoiding the use of the known biopsy kits. The main applications are in the surgical field (biopsy, infiltrations, ablations, etc.).
In the past, minimally invasive surgery mainly relied on CT imaging, followed by free-hand needle introduction based on the previously acquired images. The advent of ultrasonic imaging machines and biopsy kits allowing biopsy needles to be imaged as they were inserted in the tissue did not solve all the needle guiding problems. In many cases, CT imaging is still used because certain types of diseases cannot be imaged by ultrasound (lungs, bones), wherefore the ultrasonically guided biopsy kit is of no effective help.
Nonetheless, there undoubtedly exists the need for a needle insertion supporting tool allowing to evaluate beforehand the path of the needle, and hence its position relative to the probe plane and its path before actual insertion, because such tool would provide remarkable help, as well as technological advantage.
Also, there currently exist neurosurgery navigation systems as well as other virtual navigation systems combined with ultrasonic imaging methods. Nevertheless, these systems require an image of a pre-acquired volume, i.e. acquired prior to the surgical procedure, to be always associated with the surgical tool or ultrasonic probe.
Document WO2006/067676, discloses a method for visualizing the position of an interventional device involving the acquisition of images of an area of interest from an object displaying multiple planes that intersect. The intersection defines the position of the interventional device and the planes that identify the position of the interventional device are displayed as bounding planes. These bounding planes are displayed in a multi-dimensional display, where each plane is only rendered up to where it intersects another plane. Thanks to this only relevant portions of the data are displayed, thereby increasing the readability of the displayed image.
From the above document it is clear that at least a 3D image of the intervention area is acquired prior of carrying out the intervention and the intervention tool tracking and imaging. The orientation and the position of the tool are determined by the tracking data. The tracking system is registered with the acquired and stored 3D image data and the tracking data are used to determine the bounding planes and the image information along these bonding planes from the previously acquired 3D image data. It is important to consider that in this case volumetric (3D image data of the patient is acquired only once prior of the carrying out of the intervention, so that the determination of the interventional tool in the following intervention due to the tracking data is referred to the volumetric image data which has been acquired at an earlier instant. Considering patient movements and also natural movements of the tissues due to heart beats, breathing, etc., the reliability of the information about the relative position of the tool relatively to the a target object is relatively low.
Document WO2005/039391, seems to have considered this problem and suggests a way of solving the above problem. A method is disclosed for assisting a user in guiding a medical instrument to a subsurface target site in a patient. The method generates at least one intraoperative ultrasonic image. The method indicates a target site on the ultrasonic image and determines a 3-D coordinates of the target site in a reference coordinate system. The method tracks the position of the instrument in the coordinate system, projects onto a display device a view field as seen from the position with respect to the tool in the reference system and projects onto the displayed view field indicia of the target site corresponding to the position. By observing the indicia the user can guide the instrument toward the target site by moving the instrument so that the indicia are placed or held in a given state in the displayed filed of view.
The above disclosed method requires an endoscope for determining the images of the target site. Means for acquiring a pre-interventional 3D image which is the reference image, means for acquiring ultrasound images, an interventional tool, means for tracking the ultrasound probe, the endoscope and the interventional tool and means for registering the data from the pre-interventional volumetric image with the endoscopic image, with the ultrasound image data and with the tracking data.
The system is complex and in order to generate images corresponding to the views of a human user as placed on the tip of the tool and looking in direction of vied corresponding to a certain tool orientation, the endoscopic image is needed. Furthermore this image is a video image and not an ultrasound image which could help in see what is behind a certain surface. The ultrasound images displayed are along planes which comprise also the interventional tool image. The computational burden is considerable since the computation shall provide for registering video images of the endoscope, tracking data of the interventional tool and of the endoscope and of the ultrasound probe and the pre-intervention volumetric images and has to continuously generate images which are recalculated basing on the new position of the tool and of the target.
Each of the above methods require a pre-interventional volumetric image acquisition, which image data are used for determining the relative position of the tool to the anatomy of the interventional district and to a certain target site and cannot thus considered pure real-time methods, since a high influence in the image showing the relative position of target site and tool is given by this fact and the position inaccuracy due to systemic physiological tissue movements is still given to a high rate.
The invention has the object of providing a device and a method for guiding surgical tools by ultrasonic imaging which, using simple and inexpensive arrangements, can obviate the limitations of current surgical tool guiding and/or virtual navigation systems, while providing a better, easier and more intuitive control of the tool, with higher accuracy and in a substantially real-time mode, without involving any hardware extension image quality degradation or excessively longer scanning and processing times.
One embodiment of the invention fulfills the above object by providing a device as described hereinbefore, which comprises:
a) means for acquiring in real-time a time sequence of 3D ultrasonic images of a target area;
b) means for the contemporary real-time tracking the position and orientation of a surgical tool and means for defining in real-time the position or direction of a characteristic axis of the tool corresponding to the detected position and orientation of the tool;
c) means for determining in real-time the position of a working or functional end of the tool along said direction or said characteristic axis;
d) means for determining the relative position in space of each real-time 3D image and the real-time direction or characteristic axis of the tool corresponding to each real-time 3D image;
e) means for generating, for one or more of the real-time 3D images acquired in a time sequence, a real-time 2D image defined by an image plane that intersects the corresponding real-time 3D image of said time sequence, which real-time 2D image plane has a predetermined inclination relative to the direction or the characteristic axis of the tool determined in real-time and a predetermined distance from the working end of the tool with reference to the said orientation and position of the tool upon acquisition of the corresponding real-time 3D image, said real-time 2D image being generated using the real-time image data of the corresponding real-time 3D image of the time sequence of real-time 3D images;
g) the inclination of said real-time 2D image plane relative to the direction or the characteristic axis of the tool determined in real-time, and the distance of said 2D image plane relative to the working end of the tool being such that the real-time image generated in the 2D image plane corresponds at least approximately to a vision of the target area from the point of view of an observer situated at or near a part of the tool or said characteristic axis of the tool;
h) the image generated along said plane including indications of the position of the target to be treated by said tool and/or the position of the functional characteristic axis of said tool in said image as well as the dimensions of the tool in a direction perpendicular to said functional characteristic axis.
According to a first preferred alternative, the inclination of said 2D image plane relative to the direction or the characteristic axis of the tool, and the distance of said 2D image plane relative to the working end of the tool are such that the image generated in the 2D image plane corresponds at least approximately to a vision of the target area from the point of view of an observer situated at said working end of the tool, and whose direction of view is coincident with or parallel to the direction or the characteristic axis of the tool, whereas said 2D image includes indications of the position of the target to be treated by said tool and/or the point of coincidence of the characteristic axis of the tool with said 2D image plane and possibly also with the section of the tool along said plane.
In a second preferred alternative, the cutting plane along which the 2D image is generated is at least parallel to the characteristic axis of the tool. Possibly, this plane is also coincident with said characteristic axis of the tool. In this case, the image being displayed is similar to the image that a user would see in a direction of view perpendicular to that of the characteristic axis of the tool, whereas the position of the characteristic axis of the tool is indicated in said image by two lines parallel to said axis and situated at a distance from each other at least corresponding to the tool size perpendicular to said characteristic axis, and the position of the target to be treated by said tool is also indicated.
It is important to notice that the acquisition of the volumetric (3-D) ultrasound images is made at the same time, i.e. contemporary to the tracking of the probe and of the tool and to the registration of the tracking coordinates with the coordinates of the said volumetric images, so that the images shown on the 2D image planes is a real-time image, which time delay relatively to the effective one is limited to the time needed for the computation. Computational burden and computational times are dramatically low relatively to prior art systems particularly due to the fact that only ultrasound data are used for generating some sort of endoscopic images which are non video (i.e. surface images) and that the registration step can be carried out at the beginning of the session only once and eventually may be repeated at certain time intervals.
No endoscopic or video device is needed further to the ultrasound probe and to the tracking means.
As it will appear also from the following description using a 3-D probe reduces further the computational burden because the probe may be held at a fixed position and the tracking data to be determined are only the ones of the interventional tool.
Advantageously, the device is provided in combination with a rod or needle-like element and the characteristic direction or characteristic axis is the longitudinal axis of said rod or needle or a direction or axis parallel to said longitudinal axis, whereas the working end is the rod or needle insertion end into the target area.
A position and orientation identification and detection marker is associated with the tool, and may be advantageously arranged to be coincident with the characteristic axis or an axis parallel thereto or in a predetermined position relative thereto. Particularly in the case of a biopsy needle or the like, the marker may be located at the tip or rear end of the needle or the like.
Advantageously, according to an improvement, in order to account for and detect any bending of the tool, at least two identification and detection markers are associated therewith, which are located at a certain distance from each other along said direction or said characteristic axis or along an axis parallel to said characteristic axis. The marker/s cooperate with detection means of a system for determining and/or tracking the position and orientation of the tool relative to a predetermined reference system.
In one embodiment, the device further comprises a monitor and means for displaying images on said monitor, which means allow simultaneous, side-by-side or alternate display of images of the target area defined by at least one image plane coincident or parallel to the direction or characteristic axis of the tool and by at least one image plane having the predetermined inclination relative to the direction or the characteristic axis of the tool and the predetermined distance from the working end of the tool.
Advantageously, the sequence of 3D images is acquired by an ultrasonic probe, whereas the position in space of the acquired image relative to a reference system is determined by probe position and displacement detection systems.
Particularly a volumetric probe is advantageously used for acquiring the sequence of 3D images.
Referring to the units that compose the device of the present invention, either one of the two following solutions can be used for detecting the relative position of the probe and the tool.
In a first embodiment, the means for determining the position and orientation of the tool and particularly the biopsy needle, i.e. the characteristic axis thereof, are the 3D imaging system itself, i.e., in this special case, the means for acquiring the sequence of 3D ultrasonic images. The detected volumetric images also include the image of the tool when the latter is within the field of view, and this image of the tool is used to determine, thanks to the markers, the position and orientation of the tool, i.e. its characteristic axis, relative to the 3D image and hence the position and orientation of the tool in the anatomic region being imaged.
This technique is not limited to the ultrasonic imaging use. It can be also applied to X-ray or CT imaging. In this case the ring would be displaced instead of the patient table, and the CT images would display both the diseased tissue and the tool, i.e. the biopsy needle.
In the second embodiment, a tracking system is used for detecting the position and orientation of the probe and the tool, particularly the characteristic axis thereof. The tracking system allows the positions of the probe and tool, e.g. a needle, to be related to each other, to define the cut plane in the tool path. Several different tracking systems are current available, of either electromagnetic or optical type. The remarkable advantage of an electromagnetic system consists in that it has very small markers, consisting of micro-receivers that may be also placed at the tip of the needle. A tracking system adapted for use with a needle is the one sold by Ascension Technology with the trade name PCIBird.
These micro-receivers are used in combination with the transmitter to define the position of the probe and the needle on space and to determine the cut plane. Advantageously, two micro-receivers are associated with the needle at the tip and the rear, to accommodate any bending. Such bending would create curved surfaces formed by the volume 4D.
Concerning the tools for which the method and device of the invention are particularly suitable, these may be of the minimally invasive type, such as infiltration syringes, biopsy tools, thermoablation needles, HIFU rays. A possible method for standardizing all needle families consists in providing a custom “spindle” equipped with a receiver to be used as an insertion tool designed to be fitted with the special needle for the required procedure.
The probe, particularly of volumetric type, may be either convex or linear and will be advantageously able to generate a 3D image of the required size. The minimum volume rate required to obtain effects is 4 volumes/sec.
A volumetric probe may be as disclosed in EP 1 681 019 and in EP 1 167 996 by the applicant hereof.
The invention also relates to a method for guiding surgical tools by ultrasonic imaging using the above described device, which method includes the steps of:
a) acquiring a time sequence of 3D ultrasonic images of a target area;
b) defining a direction or a characteristic working axis for the tool;
c) defining the position of a working or functional end of the tool along said direction or said characteristic axis;
d) determining the relative position in space of each of the 3D images of the time sequence of images and the direction or characteristic axis of the tool for each of said 3D images;
e) defining, for one or more of the 3D imaged acquired in the time sequence, a plane of a 2D image which intersects the corresponding 3D image and has a predetermined inclination relative to the direction or the characteristic axis of the tool and a predetermined distance from the working end of the tool with reference to the orientation and position of the tool upon acquisition of the corresponding 3D image;
f) using the data of the corresponding 3D image of the sequence of 3D images to generate an image along said 2D image plane;
g) the inclination of said 2D image plane relative to the direction or the characteristic axis of the tool, and the distance of said 2D image plane relative to the working end of the tool being such that the image generated in the 2D image plane corresponds at least approximately to a vision of the target area from the point of view of an observer situated at or near a part of the tool or said characteristic axis of the tool;
h) the image generated along said plane including indications of the position of the target to be treated by said tool and/or the position of the functional characteristic axis of said tool in said image.
Particularly relevant for the present invention is the fact that steps a) to c) are contemporary and carried out in real time.
So each 3-D image is a real time ultrasound image and the position and orientation of the tool is also real-time and related to the corresponding 3-D image. Thus also the steps and the results of the steps indicated above with d) to h) are essentially carried out in real-time, if considering very short computational times. Thus the 2-D image displayed and corresponding to a certain plane as defined in steps g) to h) is practically a real-time image. The time shift between the effective position of the tool in the real world and the one determined by the method being infinitesimal and corresponding to the time needed by the system to carry out the computational steps.
As additional information, said image may also include indications about the dimensions of the tool in a direction perpendicular to said functional characteristic axis.
According to a preferred alternative, the cutting plane along which the 2D image is generated has such an inclination that the image being generated corresponds to the one that a user would see if he/she were situated at said working end of the tool in a direction of view coincident or parallel to the direction or the characteristic axis of the tool, whereas said 2D image would include an indication of the position of the target to be treated by said tool and/or the point of coincidence of the characteristic axis of the tool with said plane of the 2D image and possibly also the section of the tool along said plane.
Advantageously, the method is carried out in combination with tools including a rod or needle-like element and the characteristic direction or characteristic axis is the longitudinal axis of said rod or needle or a direction or axis parallel to said longitudinal axis, whereas the working end is the rod or needle insertion end into the target area.
In this case the 2D image plane may be perpendicular to the direction or characteristic axis of the tool.
In a further alternative, the cutting plane along which the 2D image is generated and displayed is parallel to and possibly also coincident with said characteristic axis of the tool. In this case, said image contains indications about a possible range for positioning the needle or tool, i.e. the characteristic axis of the needle or tool, which range is delimited by two parallel lines spaced to an extent at least corresponding to the detection accuracy of the system. In practice, the two lines delimit the image area in which the image of the tool is expected to appear.
In order to determine the position and orientation of the tool with reference to an axis and particularly to the characteristic or working axis thereof, one position detection and identification marker has to be placed on the tool in a predetermined position relative to the tool shape.
Preferably, according to an improvement, at least two identification and detection markers are associated with the tool, and are located at a certain distance from each other along said direction or said characteristic axis or along an axis parallel to said characteristic axis, which markers cooperate with detection means of a system for determining the position and orientation of the tool relative to a predetermined reference system.
As mentioned above in greater detail, several different systems may be used for determining the position and orientation of the tool relative to the image volume.
One solution consists in using the tool image that appears in the acquired volumetric images.
The second solution, which has also been described above, includes a tracking system which uses sensors or transponders on the tool and the ultrasonic probe to determine their position and orientation relative to a reference coordinate system predetermined by the tracking system itself. According to an improvement of the method of the invention, the sequence of 3D images is acquired by an ultrasonic probe, whereas the position in space of the acquired image relative to a reference system is determined by probe position and displacement detection systems.
Advantageously, the sequence of 3D images is acquired using a volumetric probe.
Considering the above characteristics of the method of the invention, such method is thus based on the concept of using the image planes generated by a volumetric probe to drive an tool, such as a needle, using a tracking system, for optimized selection of both the position of the needle relative to the probe and the image plane to be associated with the needle. In this case, the image plane of the probe may not be coplanar with the image plane of the needle.
In other words, the volumetric probe is used to generate a real-time 4D volume. The mutual positions of the probe and the needle are defined using the tracking system. These relative position coordinates are used to generate a plane to be associated with the needle, by cutting off the acquired volumes according to the needle position. A real-time image is thus obtained, which is associated with the needle. The volumetric probe is only used as a data generator, whereas the needle is used both for the percutaneous procedure and as a probe. Thus, by simply moving the needle, the user can display the target and easily select the type of insertion.
According to another characteristic, the method of the invention may provide simultaneous, side-by-side or alternate display of images of the target area defined by at least one image plane coincident or parallel to the direction or characteristic axis of the tool and by at least one image plane having the predetermined inclination relative to the direction or the characteristic axis of the tool and the predetermined distance from the working end of the tool.
Images may be also possibly displayed according to different image planes, intersecting the volumetric image with different inclinations and at different points.
In at least one of the images, the position of the tool is indicated by a symbol which is well differentiated from the image of the target area.
The above description clearly shows the advantages and differences of the method and device of the present invention as compared with standard neurosurgery navigators. In prior art navigation and guide systems, the surgical tool or the ultrasound probe is associated with an image obtained from a pre-acquired volume and not a real-time image associated with the needle.
Conversely, the present invention uses a real-time imaging source, to associate the position of the tool and the image of its path. On the other hand, the tracking system may be the imaging source itself, with the tool and its position and orientation in the imaging volume being identified in real time.
Further improvements will form the subject of the dependent claims.
The characteristics of the invention and the advantages derived therefrom will be more apparent from the following description of non-limiting embodiments, and as illustrated in the drawings.